1. Field of the Invention
This invention relates to a method and apparatus for inspecting the outer appearance of a golf ball having a multiplicity of dimples in its surface for detecting a defect on the ball surface. More particularly, it relates to a golf ball outer appearance inspecting method and apparatus capable of automatic, high-precision judgment whether or not golf ball products are to be rejected.
2. Prior Art
In the manufacture of golf balls, defects such as flaws, weld marks, gate marks (depressions left at the gate), and foreign matter inclusions can form on the surface of golf balls for some reason or another. Golf balls having such a defect are low in commodity value and will suffer from a loss of aerodynamic performance such as a short carry and less flight stability because the defect can induce turbulence during flight. It is then a common practice to carry out an outer appearance inspection on golf balls for picking up defective balls before shipping.
It has long been desired to incorporate an inspection apparatus in the manufacturing line to automate an outer appearance inspection for detecting any defect on the golf ball surface. Automatic outer appearance inspection is difficult with golf balls because of their unique surface topography. The present status of outer appearance inspection is visual observation by workers.
As a substitute for visual inspection, it is commonly employed to automatically inspect the outer appearance of various articles by taking an optical image of an object to be inspected by optical imager means such as a camera, and judging from the image determining whether or not the outer appearance is acceptable by image processing means. Where the object to be inspected is a dimpled golf ball which is a spherical article having a plurality of depressions in its surface, it is difficult to detect a defect on the surface. Since dimples are distributed on the spherical surface, the dimples appear in the image of the surface as ellipsoids having indefinite major and minor axes and additionally, these ellipsoids appear irregularly. It is then quite difficult to detect the difference between the dimple and the defect on the image for judging the presence of the defect. Precise inspection is thus prohibited.
Since golf balls are generally molded in molds, it is a common practice to apply to golf balls an indentation mark indicating a particular mold for the purpose of identifying the mold in which a ball is produced. Such an indentation mark is generally applied within a dimple. Unlike a stamp mark printed in color, the indentation mark is a symbol represented by a colorless raised or depressed portion. It is difficult to discriminate the indentation mark from the defect.
It is also contemplated to detect a change on the ball surface using a laser beam. The inspection with a laser beam adds to the cost and is thus inapplicable to golf balls which are of low price and require mass inspection within a short time.
For this reason, the state-of-the-art outer appearance inspection of golf balls relies on visual observation by workers as mentioned above. The inspection by visual observation imposes a heavy burden to workers. To visually find a slight defect on a golf ball having a plurality of dimples in its surface is a very hard work. Since the precision of judgment varies with individual workers and with the condition of a worker, sufficient precision of inspection is not always insured.